I mainly use my Nook HD to play sound effects and music clips on an FM radio show. it was doing a lot of random reboots -- usually at the worst possible times -- so I uninstalled a lot of apps, several of which had been put on by me. The tablet became stable.
Now I want to take it on a trip and watch videos on it. I put a few in the My Files > Videos folder but when I went to find the video player app, there was nothing. So I navigated to the folder and clicked on the files and received a message saying that the Nook couldn't play them, they may not be the correct format.
They are .mkv videos which I understand the Nook HD should be able to play. It's my guess that the real problem is that I uninstalled whatever app is needed to play there.
How can I (1) find out what the default video playing app is, and (2) re-install it?
I never used the default player since Nook's buit in software has usually been lacking. I suggest you download a free player from the Google Store like MX Video Player. It's a decent player and lets you play a much larger variety of file types including .mkv and has a good variety of settings as well.